Radio frames in a Long Term Evolution (LTE) system and an LTE-Advanced (LTE-A) system have frame structures in a Frequency Division Duplex (FDD) mode and a Time Division Duplex (TDD) mode. FIG. 1 is a diagram of a frame structure in an existing LTE/LTE-A FDD system. A 10 ms radio frame consists of 20 time slots each of which is 0.5 ms long and numbered as 0˜19, and the time slots 2i and 2i +1 form a subframe with a length of 1 ms. FIG. 2 is a diagram of a frame structure in an existing LTE/LTE-A TDD system. As shown in FIG. 2, a 10 ms radio frame consists of two half frames with each having a length of 5 ms. Each half frame includes 5 subframes with each having a length of 1 ms, and the subframe i is defined to include two time slots 2i and 2i+1 with each having a length of 0.5 ms. An Uplink (UL) and Downlink (DL) configuration supported in a TDD system is shown in Table 1:
TABLE 1UL-DLUL-DLswitchSubframe numberconfigurationperiod012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
For each subframe in a radio frame, “D” represents a subframe dedicated to DL transmission, “U” represents a subframe dedicated to UL transmission, and “S” represents a special subframe, including three parts, i.e. a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS).
The TDD supports the periods of 5 ms and 10 ms for switching between UL and DL. If the DL-to-UL switch period is 5 ms, both of two half frames include the special subframe. If the DL-to-UL switch period is 10 ms, only the first half frame includes the special subframe. Subframe 0, subframe 5 and the DwPTS are always configured for DL transmission. An UpPTS and the subframe following the special subframe are dedicated to UL transmission.
In DL Hybrid Automatic Repeat Request (HARQ) of an LTE system, when UE does not use a Physical Uplink Shared Channel (PUSCH) for transmission, HARQ-ACK information from a Physical Downlink Shared Channel (PDSCH) is transmitted on a Physical Uplink Control Channel (PUCCH); otherwise, the HARQ-ACK information is transmitted on the PUSCH.
In an LTE TDD system, transmission of HARQ-ACK information from a PDSCH in DL HARQ is required to follow the following timing specification, that is, a DL HARQ timing is required to follow the following specification: when UE detects transmission from a PDSCH or a PDCCH indicating DL Semi-Persistent Scheduling (SPS) release on subframe n-k, the UE transmits corresponding HARQ-ACK information on subframe n, wherein k belongs to K, M is the total number of K, a maximum value of M is 4, and values of K in different UL-DL configurations are shown in Table 2:
TABLE 2UL-DLSubframe number nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8,———————7, 5, 4, 11, 66——775——77—
In an LTE TDD system, there are two methods for transmitting an HARQ-ACK message. One is bundling, of which a core idea is that logical AND operation is performed on HARQ-ACK messages, required to be fed back on a UL subframe, of transport blocks corresponding to each DL subframe. UE is required to feed back a 2-bit HARQ-ACK message if each DL subframe has two transport blocks and the UE is required to feed back a 1-bit HARQ-ACK message if each subframe has only one transport block. The other method is multiplexing. In the LTE, the method mainly refers to PUCCH format 1b with channel selection, a core idea of which is that different PUCCHs and different modulated symbols on the channels are utilized to represent different feedback states of DL subframes, required to be fed back on a UL subframe. If there are multiple transport blocks on the DL subframes, channel selection is performed after spatial logical AND operation (also called space-domain bundling) for HARQ-ACKs fed back by the multiple transport blocks of the DL subframes, and then PUCCH format 1b is adopted for transmission.
Compared with an LTE system, the most significant characteristic of an LTE-A system is that a Carrier Aggregation (CA) technology is introduced, that is, bandwidths of the LTE system are aggregated to obtain a greater bandwidth. In a system into which the CA is introduced, a carrier to be aggregated is called a Component Carrier (CC), and is also called a serving cell. In addition, concepts of Primary Component Carrier/Cell (PCC/PCell) and Secondary Component Carrier/Cell (SCC/SCell) are further introduced. A system into which the CA is introduced at least includes a primary serving cell and a secondary serving cell, wherein the primary serving cell is in an active state all the time. The TDD system only supports, in Rel-10, aggregation of serving cells with the same UL-DL configuration.
In an LTE-A CA system, when a base station configures multiple DL serving cells for UE, the UE is required to feed back HARQ-ACK messages of corresponding code streams of the multiple DL serving cells. In the LTE-A system, when an HARQ-ACK message is transmitted on a PUCCH, two transmission manners are defined: a transmission manner of PUCCH format 1b with channel selection and a Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-s-OFDM)-based transmission manner. Since the DFT-s-OFDM-based transmission manner and its channel structure are different from those of PUCCH format 1/1a/1b/2/2a/2b, such a structure is called PUCCH format 3 in an existing LTE-A protocol. For UE configured with multiple serving cells, if the UE may support aggregation of at most two serving cells, the UE may transmit an HARQ-ACK in a manner of PUCCH format 1b with channel selection; and if the UE may support aggregation of more than two serving cells, the base station may further use high-layer signalling to configure whether the UE transmits HARQ-ACK information in the manner of PUCCH format 1b with channel selection or PUCCH format 3.
In an LTE-A TDD system, when two serving cells are configured, a manner of format 1b with channel selection is adopted to transmit HARQ-ACK information and the number M of corresponding DL subframes is 1, the transmitted HARQ-ACK information is Acknowledgement/Negative Acknowledgement/Discontinuous Transmission (ACK/NACK/DTX) feedback to a transport block of each serving cell or a PDCCH indicating SPS release. When two serving cells are configured, the manner of format 1b with channel selection is adopted to transmit the HARQ-ACK information and the number M of the corresponding DL subframes is 2, the HARQ-ACK information is an ACK/NACK/DTX response to a PDSCH of each serving cell or the PDCCH indicating SPS release. That is, if the PDSCH corresponds to two transport blocks, the HARQ-ACK information from the PDSCH is obtained by space-domain bundling HARQ-ACK information from the two transport blocks. When two serving cells are configured, the manner of format 1b with channel selection is adopted to transmit the HARQ-ACK information and the number M of the corresponding DL subframes is 2<M≤4, the HARQ-ACK information fed back by each serving cell has at most 2 bits, and is obtained by sequentially performing space-domain bundling and time-domain bundling on ACK/NACK/DTX responses from all the transport blocks of each serving cell. In a current protocol release, when two serving cells are configured, a manner of format 1b with channel selection is adopted to transmit HARQ-ACK information and the number M of corresponding DL subframes is 3 or 4, space-domain bundling and time-domain bundling are sequentially performed on ACK/NACK/DTX responses from all transport blocks of each serving cell to obtain 2-bit HARQ-ACK information of each serving cell. Transmission of the obtained HARQ-ACK information on a PUCCH or a PUSCH is implemented in the following manner.
If the HARQ-ACK information is to be transmitted on the PUCCH, PUCCH resources and transmission subframes are found in a corresponding mapping table according to the ACKs/NACKs/DTX obtained by performing space-domain bundling on the ACKs/NACKs from all the transport blocks of the serving cells, and then the HARQ-ACK information is transmitted. The mapping table is shown in Table 2 and Table 3.
If the HARQ-ACK information is to be transmitted on the PUSCH and there is no corresponding UL grant, coded input bits o(0),o(1),o(2),o(3) for transmission are found from a corresponding mapping table according to the ACKs/NACKs/DTX obtained by performing space-domain bundling on the ACKs/NACKs from all the transport blocks of the serving cells, and then the HARQ-ACK information is transmitted.
TABLE 3UL-DLconfigurationof a TDDSubframe nserving cell01234567890——6, 5, 4—5, 4——6, 5, 4—5, 41——7, 6, 55, 4———7, 6, 55, 4—2——8, 7, 5, 4, 6————8, 7, 5,——4, 63——10, 9, 8, 118, 7, 66, 5, 4—————4——12, 10, 9, 8,8, 6, 5, 4, 7——————115——13, 12, 10, 9,———————8, 7, 5, 4, 11, 66——8, 76, 76, 5——7, 65, 4—
When UE detects PDSCH transmission of an FDD secondary serving cell or a PDCCH indicating DL SPS release on subframe n-k, the UE transmits HARQ-ACK information on UL subframe n of a TDD primary serving cell, wherein k belongs to K, and when the primary serving cell has different UL-DL configurations, specific values of K are shown in Table 4:
TABLE 4UL-DLconfigurationof TDDSubframe nserving cell01234567890——6, 5, 4—5, 4——6, 5, 4—5, 41——7, 6, 55, 4———7, 6, 55, 4—2——8, 7, 5, 4, 6————8, 7, 5,——4, 63——10, 9, 8, 7, 6, 116, 55, 4—————4——12, 10, 9, 8, 7, 116, 5, 4, 7——————5——13, 12, 10, 9, 8, 7,———————5, 4, 11, 66——75, 6, 75——77, 6,—5, 4
As can be seen from Table 3 and Table 4, a value of M is at least 4 when the primary serving cell adopts TDD UL-DL configurations #2, #3 and #4, while the existing PUCCH format 1b with channel selection is only suitable for M=4. Thus, the PUCCH format 1b with channel selection cannot be used to transmit an HARQ-ACK in TDD-FDD CA.